基於IEEE 802.11e並應用於數位家庭之整合性服務品質保證機制

Abstract

隨著技術與市場的成熟，無線區域網路對於數位家庭應用開始佔有相當重要的地位。由於IEEE 802.11協定中無法提供合適的服務品質保證，IEEE 802.11e 協定被提出來以提供多媒體應用之服務品質保證。但在IEEE 802.11e之EDCA機制下，具較低優先權的資料在高優先權資料滿載的情形下，會發生餓死的現象，而此現象對於家庭網路中的http、telnet、ftp、或家電控制等應用會造成相當大的問題。DDRR 試圖改善上述問題，惟其缺點主要是無法基於實際網路狀況進行動態因應，亦無法提供確保服務品質的相關參數。因此，我們設計了一套基於IEEE 802.11e的整合機制，SPLPT。它結合了EDCA與HCCA方法，針對即將發生餓死的低優先權資料提供補償性的非競爭性頻道存取。我們的方法可以有效避免低優先權資料的餓死問題，並且在正常負載下與EDCA有相同的傳輸表現。SPLPT 整合了EDCA與HCCA兩種媒體存取方式，同時提供動態調整機制，並在完全相容於IEEE 802.11e下，提供餓死問題的解決方法，以及有良好的傳輸表現。模擬結果顯示，我們提出的整合機制與EDCA和DDRR比較，在高負載下且有較多高優先權資料的環境下，低優先權資料的媒體存取控制延遲時間，可以分別縮短3.9倍和5.1倍；就低優先權資料而言，傳輸量可由0 %提升至最高傳輸量的5 %，因此可避免造成餓死情形。

The wireless local area network (WLAN) is now one of most promising technologies to provide network connectivity for digital home applications with easy installation, and both technical and market maturity. Since legacy IEEE 802.11 standards offer inadequate QoS support, IEEE 802.11e was proposed to provide QoS support for multimedia applications. However, for the Enhanced Distributed Channel Access (EDCA) of IEEE 802.11e, when a channel is occupied with high priority traffic, low priority traffic may suffer starvation due to its little chance contending for the channel. The starvation prevention is crucial to digital home applications such as http, telnet, ftp, and home appliance control applications. The starvation of low priority traffic may result in these digital home applications in failure, which is unacceptable. DDRR was proposed to achieve this goal; however, it cannot be adapted to traffic condition dynamically. It also provides few parameters for QoS guarantee. In this thesis, we propose a QoS scheme, called Starvation Prevention for Low-Priority Traffic (SPLPT), for digital home applications in IEEE 802.11e WLANs. SPLPT prevents starvation of low priority traffic by providing adequate contention-free channel access in its compensation procedure for starving traffic (CPST) when starvation is about to occur; and it has the same behavior as EDCA when the CPST is not activated. SPLPT integrates both EDCA and HCCA to provide high throughput performance as well as starvation prevention, and it is fully compatible to IEEE 802.11e. Simulation results have shown that when the WLAN is heavily loaded with high priority traffic, SPLPT shortens the MAC delay of low priority traffic by 3.9 and 5.1 times, respectively, compared to EDCA and DDRR. In addition, the throughput of low priority traffic is raised up from 0 % to 5 % of the maximum throughput to avoid starvation.